1. Field of the Invention
The invention relates to a system and apparatus for conversion of solar radiation into microwave energy in space and conversion into low frequency electrical power utilizing solid state devices.
2. Description of the Prior Art
Conversion of microwave energy to low frequency electrical power has been disclosed in prior art embodiments utilizing antenna-rectifier arrays comprising a large number of devices, such as solid state devices, to propel space vehicles. U.S. Pat. No. 3,434,678 issued Mar. 25, 1969 to W. C. Brown et al and assigned to the assignee of the present invention provides an embodiment of a helicopter-type space vehicle which is self-supporting by means of microwave energy beamed into space and converted to electrical power for operation of an electric motor. Microwave energy is defined an electromagnetic energy in that portion of the spectrum having wavelengths in the order of 1 meter to 1 millimeter and frequencies in excess of 300 MHz. Such energy is preferred for wireless transmission since it is desirable to focus the transmitted energy with a relatively high power density upon a small area spaced from the source. In accordance with the laws of optics, the sharpness of a microwave beam varies as the ratio of antenna dimensions to the wavelength of the transmitted energy. Accordingly, for a given predetermined power density and beam sharpness, the very short wavelengths of microwave frequency oscillations facilitates a corresponding decrease in the dimensions of the antenna means for transmitting and receiving. In addition, in long wave or radio-type transmission, difficulties are encountered as a result of natural or man-made interference and noise and this problem is considerably less significant with the transmission of microwave frequencies. The recent United States space programs have shown that the employment of very short microwaves for beamed energy is preferable for penetration of certain atmospheric reflection layers, as well as, the advantages of accurate focusing and high power density of the transmitted energy.
Other examples of the utilization of microwave energy for space applications are found in U.S. Pat. No. 3,174,705, issued Mar. 23, 1965 to D. Shiff et al, as well as U.S. Pat. No. 3,083,528 issued Apr. 2, 1963 and U.S. Pat. No. 3,114,517, issued Dec. 17, 1963 to W. C. Brown. All of these are also assigned to the assignee of the present invention and disclose various conversion means utilizing heat exchangers for conversion of microwaves into electrical energy or heat which can be utilized for directly or indirectly propelling a space vehicle.
The current energy crisis throughout the world due to the growing shortage of fossil fuels, namely coal, oil and natural gas due to increases in the level of consumption and the decline in available resources has led to the search for new sources of energy. The use of solar energy has been proven in the space program to provide for electric power aboard the spacecraft. In addition, numerous attempts have been made on the earth to collect and convert solar energy into useful electrical power. An embodiment of a means for conversion of solar radiation in space into microwave energy utilizing a satellite system, including means for transmission to earth stations and conversion to electrical power is disclosed in U.S. Pat. No. 3,781,647, issued Dec. 25, 1973 to P. E. Glaser. The satellite system includes several geostationary satellites positioned in an energy receiving relationship to the sun. The solar energy conversion means include guidance and control means to correctly orient the collector means in relationship to the sun. The solar energy conversion means convert the radiation received into DC electrical energy which is subsequently utilized to operate high power generators of microwave energy for transmission by means of a focused beam to collection means on earth.
Solar energy offers an almost unlimited source for man's energy needs with the economics playing the most significant role in its utilization. In recent years solid state lasers and semiconductor devices for conversion of radiant energy into electrical energy have achieved very high efficiencies. Such semiconductors include PN silicon junction diodes which can be electrically biased to operate in the current multiplication region and the generated current then becomes directly proportional to the quanta of impinging light energy. The present invention describes a unique system and apparatus for generation of microwave energy from solar radiation in space applications utilizing controlled coherent light beams and semiconductor electrical conversion means.